1. Field of the Invention
This invention relates to the suspension of surface casing inside conductor pipe in oil and gas wells, and more particularly, to a casing hanger device designed to expedite the cementing of the surface casing inside the conductor pipe and the cutting of the casing prior to the setting of the cement in order to facilitate mounting of a blow-out preventer stack on the surface casing in a relatively short period of time.
2. Description of the Prior Art
Conventional cementing of surfacing casing inside conductor pipe requires the suspension and cementing of a desired length of casing at a specified depth in the well. A length of conductor pipe is first run into the well to a specified depth, and the surface casing is subsequently suspended inside the conductor pipe, with cement pumped in the annulus between the conductor pipe and the surface casing prior to cutting the casing and mounting blow-out preventers on the casing. Typical of the methods for achieving the objective of suspending surface casing in a well is the technique set forth in U.S. Pat. No. 3,561,531 to Terrell V. Miller. This patent is directed to a method for suspending well pipe strings in wells which are particularly susceptible to subsidence of adjacent earth formations. A rather critical procedure in such a casing suspension technique is the cementing of the casing to the well bore. A period of from at least one to about twelve hours is generally necessary to permit the cement to securely set before cutting the casing and nippling up the blow-out preventers. Cutting the casing prior to a specified cement setting time frequently causes the cement bond to the casing or well bore to be broken, a condition which can be quite dangerous in the event of a "blow-out" or release of high pressure gas from the well to the surface. Conventional casing hangers are generally designed to seal the annulus between the surface casing and production casing, and are insufficiently tapered and too expensive to be used to secure surface casing in suspended position inside the conductor tubing to sufficiently stabilize the casing.
In the course of drilling relatively deep wells, after the conductor pipe is set a casing hole of selected diameter is drilled and casing of selected size is run in the hole. Cement is then pumped in the annulus between the casing and conductor pipe, and drilling begins after the cement sets. If the cement is not dry and strong, it frequently breaks due to the rotary action of the drill pipe string, and this "wobbling" and vibrating action wears the casing. In extreme cases, the drilling may wear a hole in the casing.
Accordingly, it is an object of this invention to provide a new and improved casing hanger and stabilizer which is characterized by a pair of wedge-shaped slips designed for mounting on the casing string and supported by the conductor casing to suport and stabilize the casing string while the casing concrete is setting and to permit the casing to be cut at a point between the casing hanger and the rig floor.
Another object of the invention is to provide a casing hanger and stabilizer which serves the dual function of supporting a string of surface casing and stabilizing the casing during drilling to prevent the casing from "wobbling" and vibrating due to rotation of the drill pipe.
Yet another object of the invention is to provide a new and improved casing hanger which includes a pair of matching, wedge-shaped slips which are designed to wedge in the top of a length of conductor pipe after the pipe is cut, and to support and stabilize a string of surface casing after the casing cement is pumped and prior to cutting the casing in order to facilitate mounting of the blow-out preventer stack.
Another object of the invention is to provide a new and improved casing hanger which is characterized by a pair of wedge-shaped slip segments designed for positioning in the conductor pipe by wedging the slips in the conductor pipe opening, and fitted to receive and suspend a length of surface casing inside the conductor pipe after cementing of the surface casing to the well bore and conductor pipe.
Another object of this invention is to provide a new and improved, wedged casing hanger and stabilizer which wedges in one end of the conductor pipe to suspend a length of surface casing inside the conductor pipe and undisturbed in cement to permit the surface casing to be cut prior to the 1 to 12 hour setting time generally required in the casing-setting operation.
Yet another object of this invention is to provide a new and improved, wedge-shaped casing hanger and stabilizer which is simple in design and which utilizes the conductor pipe as a bowl, and which is designed to grip and suspend the surface casing inside the conductor pipe during or after the cementing operation.
Yet another object of this invention is to provide a new and improved casing hanger and stabilizer for suspending and stabilizing surface casing inside the conductor pipe of a well after the cementing of the surface casing to the conductor pipe and the well bore, which casing hanger is generally wedge-shaped and is provided with a plurality of slots longitudinally machined in the two slip segments to permit drilling mud or other fluid to be pumped through the annulus between the conductor pipe and the surface casing prior to the setting of cement or during the drilling operation.
A still further object of the invention is to provide a new and improved casing hanger and stabilizer which is characterized by a pair of wedge-shaped slip segments having mating faces which may be removably joined by a pair of plates to suspend and stabilize a string of surface casing inside a conductor pipe for the purpose of first cementing the surface casing to the well bore or conductor pipe, then cutting the surface casing prior to setting of the cement, and subsequently stabilizing the surface casing during the drilling operation.